In door jambs heretofore used with low-temperature compartments, such as, commercial walk-in coolers and freezers, they have typically been made of a metallic material the use of which gives rise to a number of disadvantages. Such materials as aluminum and steel scratch easily, have a tendency to rust, or corrode, and due to their high thermal conductivity require a large input of heat in order to maintain the door gaskets used with the doors in a good sealing relationship and prevent condensation from forming around the perimeter of the door opening. Obviously, if the door seal is not maintained, there could result a substantial frost build-up due to outside air leakage. For example, it has heretofore been found that in order to maintain the requisite sealing conditions at the door jamb and condensation, free condition around the door opening perimeter, there has been required an input on the order of 10 watts per foot in order to insure that the door sealing gaskets are maintained sufficiently pliable to maintain a satisfactory seal where metal door jambs have been used and at the same time keep the outside perimeter of door opening at room temperature, or slightly higher, in order to prevent condensation. This is necessary to maintain adequate heat in the contact areas due to the rapid dissipation of heat through the metal. In addition to this, of course, due to the high thermal conductivity of metal, there is the substantial transfer of heat to the internal area of the cooler, or freezer, which requires additional cooling action within the low-temperature compartment to retain the cooler or freezer at the requisite temperature.
In accordance with the present invention, there is provided a door jamb that has an exterior surface made of a reenforced fiberglass material which has a high impact resistance on the order of 25 times that of an equal section of aluminum and more than 16 times that of steel. The fiberglass material does not scratch easily, but even if scratched, due to the total impregnation of color, the scratches are not readily apparent. Of very significant importance is that fiberglass has a low thermal conductivity.
Furthermore, in the event of damage to the fiberglass, it can be easily repaired by the utilization of body putty. This material is very rugged and durable and employs a thermoset resin in its manufacture. In this way, the material will not crack when it gets cold, or melt when it gets too warm. Similarly, it will obviously not rust or corrode, or degrade over the years, as some other materials have a tendency to do.
Other advantages include the reduction of weight resulting from the use of fiberglass without sacrifice to the strength and dimensional stability of the door section. Also, this material selection permits the use of steam cleaning without worry of melting or deformation, as would be the case if a thermal plastic material was used.
When a door jamb of the aforementioned type is used, due to its low thermal conductivity, there need only be employed a heater strip isolated by the door jamb from any metallic portion of the cooler or freezer consisting of a heater wire for maintaining the requisite conditions for door sealing that consumes electric power on the order of 2 watts per foot, as compared with 10 watts per foot, when one uses a metal door jamb.
On a yearly basis, the savings due to the need to only require a very low wattage in the isolated heater strip, combined with the reduced amount of heat transmitted to the inside of the cooler, are as much as $100.00 per year in electrical costs for every 36 .times. 78 inch door provided on a walk-in cooler, or freezer.